Refrigerating apparatus



Jan. 30, 1962 3,018,544

C. C. WHISTLER, JR

REFRIGERATING APPARATUS Filed April 29, 1957 2 Sheets-Sheet 1 /0- v g HINVENTQR. Ozarks C W/zifiler, Jx BY ZM HIS ATTORNEY Jan. 30, 1962 FiledApril 29, 1957 c. c. WHISTLER, JR 3,018,544

REFRIGERATING APPARATUS 2 Sheets-Sheet 2 IN VENTOR.

' Charles C FYI/Bile); J):

/' //.5 ATTORNEY United States Patent 3,018,544 REFRIGERATIN G APPARATUSGharles C. Whistler, Jr., Dayton, Ohio, assignor to General MotorsCorporation, Detroit, Mich, a corporation of Delaware Filed Apr. 29,1957, Ser. No. 655,725 2 Claims. (Cl. 29-1573) This invention relates torefrigerating apparatus and more particularly to an improved form ofrefrigerant evaporator and the method of making the same.

One of the big problems in designing window air conditioners, automobileair conditioners and the like is that of keeping the size of thecomponents at a minimum. In the case of the window units, thedesirability of reducing the size of the various components and inparticular the evaporators and the condensers has long been recognizednot only from the aesthetic point of view, but also from a practicalstandpoint as many windows are not large enough to accommodate a largeair conditioning unit. The problem of maintaining the size of thevarious units at a minimum is even more acute in automobile airconditioning systems wherein both the weight and size of the equipmentmust be maintained at a minimum.

It is an object of this invention to materially decrease the size of arefrigerant evaporator without reducing its capacity.

Still another object of this invention is to provide an evaporatorhaving wire fins both internally and externally.

- A further object of this invention is to provide an improvedarrangement for handling the wires from which the fins are made bothduring the bending of the Wires and during the brazing operation. Moreparticularly it is an object of this invention to utilize a plasticmaterial for holding a plurality of wire fins in parallel spacedrelationship while the wires are being corrugated and while the wiresare being assembled relative to the tubing and brazed to the tubing.

Still another object of this invention is to provide an improvedarrangement for brazing wire fins to a heat exchange-r in a manner so asto reduce the voids between the wire fins and the tube and so as toprevent the brazing material from bridging between or hanging onvertical sections of the wire fins.

Further objects and advantages of the present invention will be apparentfrom the following description, reference being had to the accompanyingdrawings, wherein a preferred form of the present invention is clearlyshown.

In the drawings:

FIGURE 1 is a plan view of a heat exchanger constructed in accordancewith the invention;

FIGURE 2 is a side elevational view of the evaporator shown in FIGURE 1;

FIGURE 3 is a fragmentary sectional view on an enlarged scale showingthe wire fins in a fin forming die;

FIGURE 4 is a fragmentary sectional view on an enlarged scale showingthe manner of holding the wires in parallel spaced relationship;

FIGURE 5 is a view similar to FIGURE 4 but showing a modificationthereof; and

FIGURE 6 is a fragmentary sectional view on an enlarged scale takensubstantially on line 6-6 of FIG- URE 1.

For purposes of illustration there is shown a heat exchanger of the typesuitable for use as an evaporator in a window air conditioning unit orthe like whereas certain aspects of the invention are equally applicableto refrigerant condensers and heat exchangers of other types.

One of the big problems in designing a heat exchanger is that ofproviding an adequate amount of fin surface 2 to rapidly transfer theheat between the fluid within the tubing to the fluid flowing externallyof the tubing. Another problem is that of maintaining the resistance toair flow over the fin surface at a minimum. Not withstanding the factthat it has long been recognized that wire fins are eflicient both fromthe standpoint of heat transfer and also from the standpoint of offeringa minimum amount of restriction to the flow of fluid thereover, wirefins have not been used extensively due largely to the problem ofattaching the fins to the conduits of the heat exchanger.

Referring now to the drawings, wherein a preferred embodiment of theinvention has been shown, reference numeral 10 generally designates aheat exchanger having a pair of headers 12 and 14 between which a seriesof fluid conduits 16 are arranged as shown. In the evaporatorconstruction illustrated in the drawing the conduits 16 are arranged tolie horizontally between the headers 12 and 14. The refrigerant entersthe header 14 through the line 18 and is adapted to leave through theline 20.

In the heat exchanger shown, a first set of external parallel wire fins22 is provided as shown in FIGURE 1 between adjacent sections of thefluid conduits 16. These fins help to transfer the heat between thefluid flowing over the outside surfaces of the conduit 16 and the fluidflowing within the conduit 16. A second set of internal wire fins 24 isprovided within the conduit 16. The fins 24 not only increase theturbulence of the fluid flowing through the conduit 16, but also serveto facilitate the heat transfer as well as serving to hold the tube 16from becoming distorted when pressure is applied to the walls of thetubing.

As best shown in FIGURES 4 and 5 of the drawing, the wires 22 which areused in manufacturing the wire fins are held in a predetermined spacedparallel relationship by means of membranes or strips of plasticmaterial 26 and 28. The membranes 26 and 28 are preferably sheets ofpolyethylene. For purposes of illustration there is shown an arrangementin which a first polyethylene sheet 26 has placed thereon a plurality ofparallel fins 22 and thereafter a second polyethylene sheet 28 is placedthereover and by the application of heat or by the use of suitablebonding agents, the sheets 26 and 28 are bonded to one another at thepoints 30 and, if desired, to the wires themselves. The resultingassembly is then placed between a pair of forming dies 32 and 34 whichserve to corrugate the wires with the base portion 38 of thecorrugations being flattened so as to increase the available surfacecontact between the base portions of the fins and the walls of the fluidconduits 16-. The process used in forming the external fins is much thesame as the process used in forming the internal fins except that theinternal fins are shorter than the external fins. FIGURE 3 shows thedies used in forming the internal fins.

FIGURE 5 shows a slightly modified arrangement for holding the fins inspaced parallel relationship. It is now well known that it is possibleto pass parallel wires through an extruding die which serves to extrudeplastic coating on the wires and to provide a connecting web of plasticbetween adjacent wires. Such processes are now commonly used inextruding insulated wires for electrical purposes and need no furtherdescription as no novelty is predicated on the extrusion process per se.FIGURE 5 of the drawings shows wires 22 which have a polyethylenematerial 40 which not only coats the wires but also includes webportions 42 which hold the wires in spaced relationship. The assemblyshown in FIG- URE 5 would be processed the same as that described inconnection with forming corrugations in wires that are held together asshown in FIGURE 4 of the darwings.

It has been found that the polyethylene material is particularlysuitable for this purpose in that it burns almost 100% during immersionof the heat exchanger assembly in a 1000 F. ambient without leaving anobjectional residue. In manufacturing the heat exchanger shown a firstset of corrugated fins are inserted within the tube section 16 and asecond set of corrugated fins are arranged between the adjacent tubesections 16 as shown in FIGURE 1. The tube sections 16 are then arrangedto extend through suitable apertures in the header sections 12 and 14 inaccordance with usual practice and then the entire assembly is heated toa temperature of 1130 F. The tubing 16 is of the type provided with aclading or a brazing alloy material both on its outer surface and on itsinner surface whereby upon heating of the asembly to the above mentionedtemperature the clading material serves to melt and braze the baseportions of the fins to the walls of the tubing.

By virtue of the above described construction and process the brazingmaterial is concentrated at the point where it is needed and no excessbrazing material is left for coating the projecting wire fins or forblocking the space between the fins.

Insofar as certain aspects of the invention are concerned, the brazingmaterial could be in the form of a coating on the wires or it could beseparate from either the wires or the tubing. Thus it could be in theform of a thin ribbon, a wire, or powder placed adjacent the points ofcontact between the wire fins and the tubing.

The corrugations may be formed in the wires in any suitable manner suchas by passing the wires between teeth on forming gears having teethdesigned to corrugate the wires and simultaneously flatten the baseportions of the corrugations. The flattened portions of the wires in-.

crease the area of contact between the fins and the tubing and'alsoserve to reduce the obstruction of the wires to the flow over the wirefins.

After the internal wire fins 24 have been corrugated and assembledWithin the tubing 16, the polyethylene material used for initiallyholding the wires in place during processing and assembly may be removedby chemically dissolving the polyethylene coating before the brazingoperation whereby no residue of any kind will remain within the heatexchanger. Some or all of the polyethylene material on the external wirefins could also be removed by the use of a solventif desired.

Any suitable plastic, such as polyvinyl chloride or'polyvinyl acetatecould be used in place of the polyethylene for holding the wires inplace during processing. Any suitable solvent such as methanol, benzene,ortoluol couldbe used for dissolvingthe plastic used for holding thewires in place during the initial assembly of the heat exchanger.

While the form of embodiment of the invention as herein disclosedconstitutes a preferred form, it is to be understood that other formsmight be adopted, as may come within the scope of the claims whichfollow.

What is claimed is as follow:

1. The method of manufacturing a heat exchanger which comprises holdinga set of parallel wires in spaced parallel relationship by means ofnon-metallic heat decomposable material, forming corrugations in saidset of wires and simultaneously flattening the base portions of saidcorrugations, placing said set of wires adjacent the outside wall of aconduit with base portions of said corrugations in contact with theexternal surface of said conduit in the presence of a fusible brazingmaterial, and thereafter applying heat to said asembly so as todecompose said wire holding material and fuse said wires to the walls ofsaid conduit.

2. The method of manufacturing a heat exchanger which comprisesextruding a web of decomposable material about a set of parallel wiresso as to hold said wires in spaced parallel relationship, formingcorrugations in said set of wires and simultaneously flattening the baseportions of said corrugations, placing said set of wires adjacent a wallof a conduit with the base portions of said corrugations in contact withthe surface of said conduit and in the presence of a fusible brazingmaterial, and thereafter applying heat to said assembly so as todecompose said wire holding material and fuse said wires to the wallof-said conduit.

References Cited in the-file of this patent UNITED STATES PATENTS1,780,732 Young Nov. 4, 1930 1,881,610 Hyde Q Oct. 1 1, 1932 2,328,302Simison Aug. 31, 1943. 2,500,501 Trumpler Mar. 4, 1950 2,505,619 HolmApr. 25, 1950 2,537,797 Simpelaar Jan. 1, 1951 2,573,161 Tadewald Oct.30, 1951 2,585,443 Cox Feb. 12, 1952 2,595,457 Holm May 6, 19522,596,285 Peters May 13, 1952 2,678,808 Gier May 18, 1954 2,807,074Schroeder Sept. 24, 1957 2,869,222 Whistler Jan. 20, 1959 2,916,055Brumbach Dec. 8, 1959

